The present invention relates to a gas turbine electric powerplant, and more particularly to a system for controlling a turbine engine used to operate the powerplant. The powerplant uses a turbine engine, such as an aircraft engine, to operate an electric generator that produces electric power. The system of the present invention ensures that the speed of the turbine engine will not exceed a safe limit should the load on the turbine engine be dropped. The system of the present invention allows the powerplant to be operated safely in an unattended condition.
There are numerous situations wherein it may be desirable to use a powerplant of the present invention. For example, it may be necessary to provide electrical power to a remote area that is not supplied by a utility company. Electric power consuming: operations that are commonly conducted in remote areas include, for example, drilling for oil and natural gas. Such operations may require more power than can be supplied by typical gas or diesel generators. When such an operation is too remote to receive power from a utility, the powerplant of the present invention may be used to supply electric power to the operation. Similarly, the powerplant of the present invention can be used when electric power production is required on only a temporary basis. For example, in the above-described remote drilling operation, utility power may be available, but the cost may be prohibitive based on the short period of time during which electric power will be required. Such a situation may also occur during large-scale, remote construction projects.
The power plant of the present invention may also be used to provide backup power during interruption of electric power supplied from a utility or other source. The powerplant of the present invention may be brought online in as little as 30-60 seconds, thereby preventing long periods of down time. Use of the powerplant for backup power may be highly effective for commercial buildings, manufacturing facilities, hospitals, or other locations wherein a long term interruption of electric power is particularly problematic.
One or more of the powerplants of the present invention may also be used in a variety of ways by a producer of electric power. For example, an electric utility may utilize one or more of the powerplants to provide load-leveling or peak shaving during periods of high demand for electric power. Utilities commonly struggle with the problem of meeting peak demand, which occurs typically at particular times of the day, and is usually more severe during certain times of the year. Peak demand is the result of consumers using more electricity at particular times of the day than at others; for example, during the waking hours as opposed to during the nighttime hours. To meet peak demand, power plants must typically be overdesigned—meaning that they only run near peak efficiency during periods of high demand. Therefore, for the majority of a given day, the power plant runs at a reduced output and, unfortunately, a lower efficiency. By employing the powerplant of the present invention, utility power generating plants could be designed to meet only average demand while running at optimum efficiency. One or more of the power plants of the present invention could then be tied to the utility's distribution grid, and when peak demands arise, the powerplants can be operated to inject additional electric power into the grid. The control system of the powerplant of the present invention can provide for automatic start-up and operation when high demand is detected. When the demand ebbs, the powerplants can be shut down as needed. The portability of the powerplant of the present invention also allows additional units to be set up at a utility if needed to meet increasing peak demand. Such a situation may occur when a particular area or areas served by a utility grows at a faster than expected rate. In this manner, both the cost of building a utility plant and the cost of producing electricity may be reduced, while still ensuring that peak demand can be met.
The powerplant of the present invention can also be used as a source of co-generation electric power. For example, the powerplant may be installed at an industrial facility and tied into the facilities electric power transmission and distribution system in order to augment the electric power supplied by an electric utility company. The cost to purchase electric power from a utility may vary throughout a given day or week. For example, it is common for large industrial facilities to limited in the amount of power they may use, or to otherwise be charged a significantly elevated price during periods of high demand. Such may occur, for example, during periods of extreme weather, when the general consumption of electric power typically increases. When such a situation exists, the industrial facility may operate one or more of the powerplants to supplement the electric power it receives from the utility. In this manner, the industrial facility can avoid having to either reduce its power consumption or pay a higher cost for electric power during such periods. The hot exhaust from the turbine engine may also be harnessed to provide heat or power to other devices.
The powerplant of the present invention can also be used as a source of distributed power generation. As certain populated areas grow, the demand for electric power generally increases. Many times, the provider of electric power does not have the capacity to meet the increased demand. For this reason, electric utilities often form cooperatives, or otherwise enter into agreements wherein electric power may be sold and delivered between the utilities. Thus, if one utility cannot meet demand, and a second utility has excess capacity, the second utility may sell blocks of power to the first utility. The first utility may be at a disadvantage, because the cost to purchase and transfer the electric power to the area of demand may be high. The second utility is able to take advantage of its excess capacity by selling and distributing the electricity to other providers. The powerplant of the present invention can be used to take advantage of growing markets, by allowing a provider to produce additional electric power that may be sold to other providers without sufficient capacity. Alternatively, the powerplant of the present invention may be used by a provider to obviate the need for purchasing additional electric power from another utility. Rather, the provider may use the powerplant to produce incremental electric power in small blocks, minimizing large incremental power block purchases from other utilities. The powerplant can be located to provide electric power wherever it is needed. For example, the powerplant may be placed at a distribution substation and tied into a utility's transmission and distribution lines.
The powerplant of the present invention uses a gas turbine engine to run an electric generator. More specifically, the powerplant uses an aeroderivative gas turbine engine, such as is designed for a helicopter. The turbine engine may be purchased new, or may be removed from an aircraft and retrofitted for use in the powerplant. Although a variety of turbine engines may be employed, preferably the turbine engine is a turboshaft engine. Gas turbine engines may produce in excess of 1,000 horsepower and significant torque. It has been found that turbo shaft engines are easier to harness than are turbo thrust engines.
A gearbox is preferably used to reduce the output speed of the turbine engine to a predetermined value. While the turbine engine may have an internal gear reduction, an external gearbox is typically required to obtain the proper input speed to a generator. It is possible to use a gearbox with either a fixed or variable speed reduction. The input of the gearbox is connected to the output shaft of the turbine engine by a specialized coupling.
The output shaft of the gearbox is connected to the input shaft of an electric power generator, such as a permanent magnet generator, by a specialized coupling. Rotation of the generator's input shaft and windings produces electric power that can be output to a specific load or into the power grid of an electric utility. The generator can be selected to provide the desired voltage and power output. For example, in one embodiment, the generator may produce approximately 1.2 MW of power at 480 volts.
As can be seen from the foregoing, the various uses for the gas turbine electric powerplant of the present invention may include the need to operate the powerplant in an unattended state. Thus, it is critical that the turbine engine be automatically shut down should it become disconnected from its load. The control system of the present invention operates to automatically shutdown the turbine engine if its speed exceeds a predetermined limit, such as due to a failure of the gearbox or generator. The main control system of the gas turbine electric powerplant is microprocessor based system that is preferably able to monitor a multitude of powerplant conditions, such as fuel flow, various temperatures, turbine speed, and many other conditions. The control system may be PC-based. The control system and its associated software provides for real time control and trend capabilities, based on the monitored conditions and on user settings. Additional, mechanical control systems are provided to ensure that the turbine engine can be slowed if a no-load situation occurs.
In conjunction with the main microprocessor-based control system and software, two particular mechanical systems are provided to control the gas turbine engine should it become disconnected from its load. These systems enable the gas turbine electric powerplant to be safely operated in an unattended condition. Because of the high rotational speed of the gas turbine engine, should the load connected thereto be suddenly removed, such as due to, for example, a broken coupling, a gearbox failure, or other causes, the rotational speed of the gas turbine engine could quickly exceed safe operating limits. Thus, a sudden and unexpected removal of the load will often cause the turbine engine to enter what is commonly referred to as an “overspeed” or “runaway” condition. If nothing is done to slow the turbine engine, the result of such a condition may be the failure of the engine and possibly other components connected thereto. More catastrophically, the high rotational speeds that may result, can cause the turbine engine to disintegrate, destroying the engine and endangering persons and other equipment in the area.
In the gas turbine electric powerplant of the present invention, should the load on the turbine engine caused by driving the gearbox and generator be suddenly dropped or significantly reduced, action must be taken very quickly to prevent the turbine engine from entering into an overspeed condition. To this end, the gas turbine electric powerplant employs both a compression relief system and an air directing system to control the speed of the turbine engine in the case that an overspeed condition is detected.
The gas turbine engine that is contemplated for use in the present invention is preferably a split shaft, or free power turbine engine—meaning that the turbine engine has separate, and mechanically independent gas producer and power turbines. The turbine engine is also of the turboshaft variety, meaning that the power turbine within the engine is coupled, either directly or through a reduction gearbox, to an output shaft. When an overspeed condition is detected by control software monitoring the gas turbine electric powerplant, the air directing system operates to slow down the turbine engine by affecting the angle at which incoming air is fed to the gas producer (compressor) turbine. In conjunction with operation of the air directing system, the compression relief system acts to slow down the turbine engine by removing incoming air needed for combustion and subsequent powering of the turbines. Consequently, even if the gas turbine electric powerplant is operated in an unattended state, safe shutdown of the turbine engine in response to an overspeed condition can be accomplished.
The gas turbine engine is designed to operate on both liquid and gaseous fuels that can provide a sufficient BTU output. Specific microprocessor-controlled fuel valves are provided based on the type of fuel that will be used to run the gas turbine engine. The fuel valves may be changed if it is desired to change the type of fuel used with the powerplant. The microprocessor-based design of each type of fuel valve allows the valve to communicate with and respond to instructions from the microprocessor-based control system.
The assembled components of the gas turbine electric powerplant preferably reside on a common base, such as on a transportable skid. The assembled components of the gas turbine electric powerplant may also be installed to a permanent structure, such as the floor of a factory. In the transportable version of the gas turbine electric powerplant, a specialized frame is mounted to the skid and designed to receive and restrain the turbine engine. The frame is designed to maintain the centerline of the turbine engine despite the thermal expansion thereof during operation. The size and weight of the gas turbine electric powerplant components and skid allow it to be transported by truck to virtually any site where electric power is needed. Therefore, the gas turbine electric powerplant of the present invention provides for a portable source of significant electrical energy production that may be utilized to meet a number of consumer needs.